After a grueling and costly primary, Ernst — who already struggled with campaign fundraising — starts a general election campaign against a cash-flush Democratic nominee, Rep. Bruce Braley. Ernst's primary bid was heavily boosted by third-party groups — support Republicans hope will resume as quickly as possible.

For example, less than 24 hours after the Republican's win, Braley debuted a statewide television ad attacking her for being all talk about cutting spending without having the legislative record to back it up. www.youtube.com/watch?v=b3lwSSTEvNU&feature=youtu.be

The buy has no end date, and the sum of money behind it is “significant,” said the Braley campaign.

“Ernst is vulnerable now because she doesn’t have an ability to respond to an attack in kind,” said Craig Robinson, former Iowa GOP political director and the editor-in-chief of The Iowa Republican.

Democrats have used this tactic before with success. In a 2012 Senate race in Wisconsin, former Gov. Tommy Thompson emerged from a competitive three-way primary to a barrage of ads from Democrats. It worked; Thompson lost by more than 5 points. In 2010, Democrats similarly pummeled another newly-minted, cash-poor GOP nominee, Sharron Angle, in Nevada, paving the way for a vulnerable Senate Majority Leader Harry Reid to win re-election.

Braley has a huge monetary advantage over Ernst, although it's unclear how much.

But according to pre-primary reports that included fundraising up to May 14, Ernst reported $350,000 in the bank. Braley reported $2.3 million cash on hand at the same time.

Braley ran uncontested in his primary, so he did not need to spend any of that to overcome a primary opponent. What's more, he has a track record as a strong fundraiser.

Ernst, on the other hand, posted tepid fundraising during the primary, and outside groups did much of the heavy lifting to keep her on the air. In the final weeks of her campaign, Marco Rubio’s Reclaim America PAC spent $150,000 on television ads touting Ernst, the U.S. Chamber of Commerce spent $500,000, and Senate Conservatives Action spent $100,000. Now she has about $125,000 in the bank, an Ernst campaign senior advisor told CQ Roll Call. The source said money has been coming in at a faster clip than during the primary, but acknowledged Braley currently has a financial advantage.

Republicans have already pleaded for third-party spending for Ernst to continue after the primary.

“The outside groups that were so influential in the final stretch of the primary need to remain committed to Iowa,” said former Iowa GOP Chairman Matt Strawn. “This is a winnable seat, and while Ernst is replenishing her campaign coffers, those groups can both help introduce Joni to the general election electorate and further define Braley and expose his record as out-of-touch with Iowans.”

Those outside groups not only boosted Ernst in the primary, they also forced the Braley campaign’s hand to air spots during the GOP primary.

Last week, the Braley campaign began running television ads in which the four-term Democrats touts how his legal career has allowed him to help people. The ad comes after Braley drew criticism for a comment caught on camera in which he denigrated Sen. Charles E. Grassley, R-Iowa, as just “a farmer who never even went to law school.” He later apologized .

Braley campaign general consultant Jeff Link said that kind of introductory ad was something they always planned to do because Braley is unknown in much of the state, but they had not necessarily planned to begin running those ads before the primary was over.

“The thing that changed the timing was the fact that all the outside groups started spending in the Republican primary and gave us the idea that there’s going to be no time after the primary to try to run positive media without getting attacked,” Link said.

“To be honest,” Link said, “It’s frightening. I have never seen spending by outside groups in a primary before — certainly not at this level.”

Link predicted that neither Ernst nor Braley “will be the loudest speaker in the fall. I think the outside groups will spend more than either candidate.”

None of the groups that backed Ernst have made specific commitments for the general election yet, but indicated that they would stay involved.

“The Iowa senate race is one of the Chamber’s top priorities for 2014,” said Rob Engstrom, national political director at the U.S. Chamber of Commerce.

In an email to supporters, Senate Conservatives Fund wrote, “We must do everything we can to push Joni Ernst on to victory.”

Americans for Prosperity — which does not back specific candidates — already ran an ad attacking Braley for his support for Obamacare. AFP Iowa director Mark Lucas said they would continue to hold him accountable and there could be more ads coming.

Braley will also have at least one outside group helping him: Billionaire Tom Steyer’s group, NextGen Climate, has committed to helping Braley in the race. During the primary, they ran ads attacking Ernst and one of her Republican opponents, Mark Jacobs.

But with Braley already on the air attacking Ernst, money speaks louder than words. To help Ernst keep her momentum coming out of the primary, some of these groups will have to put up the funds — and quickly.

The race is rated Leans Democratic by the Rothenberg Political Report/Roll Call.

Editor's note: This post was updated to include new financial information from the Ernst campaign.